The invention is in the field of recycling. More particularly the invention is in the field of processing steel scrap that has been contaminated with asbestos.
Asbestos is known as a material used in construction to provide mechanical strength and fire resistance. Because of its low thermal conduction capabilities and therefore its heat and fire resistance, it has been incorporated in a wide variety of constructions in various forms, amongst others in the sectors of building construction and mechanical engineering.
In the recent decades it has become clear that asbestos causes health problems such as asbestos lung disease (asbestosis), lung cancer and malignant mesothelioma. Therefore the use of asbestos has been banned in almost all countries. To date a vast amount of obsolete constructions still contain asbestos. When such constructions are to be disposed for destruction or recycling it is very important that the asbestos contained therein is disposed of in a safe manner.
Because of the safety hazards, asbestos disposal should be carried out with utmost precautions. The current disposal of asbestos containing materials comprises disposing thereof in special regulated dumping sites. This disposal methodology requires large disposal volumes, especially if the asbestos is present in other objects, such as pipes covered with asbestos or pieces of metal to which asbestos is attached, e.g. by an adhesive.
An alternative is to dissolve the asbestos, for instance in an alkaline solution. This prevents airborne contamination/inhalation of asbestos fibers. However, it is very difficult to operate a process involving dissolving asbestos to separate it from asbestos containing material in an economically feasible way.
EP-A-1 277 527 discloses a method to dispose of asbestos, which involves placing the initial product as pieces in a tunnel oven at a temperature of between 600° C. and 1000° C. for drying the asbestos fibres. This is followed by mechanical comminuting to produce a secondary raw material without asbestos for the cement industry. The disadvantage of this method is that it requires a considerable amount of energy. Also the method it not suitable for processing steel material that contains asbestos.
JP-A-2004/204261 describes a recycling method for scrap of building materials generated on a dismantling field in which iron resources can be recovered. According to this known method contaminated scrap is classified in fractions including resin content scrap and asbestos content scrap. The asbestos containing scrap is charged in small quantities in a processing furnace, which is filled with molten iron obtained from an essentially non-contaminated fraction. The classification of the different fractions requires handling, which may result in asbestos being emitted into the environment. Moreover, according to this known method only small quantities of 2 tons or less of asbestos contaminated steel can be processed by mixing it in an existing steel melt.
US-A-2007/0251607 describes a process for handling fragments that are contaminated with asbestos, which requires a step of coating the fragments to immobilize the asbestos particles. Coating the fragments is an extra step, requiring extra handling, which increases the risk of asbestos particles being emitted into the atmosphere.
WO-A-98/03830 describes an approach for melting a railway car contaminated with asbestos, which involves the entire railway car being put into a melting unit. No measures are described to avoid spreading of asbestos into the environment.
WO-A-97/33840 describes processing asbestos containing waste in a vitrification method. The materials are bagged in plastic bags, which are subsequently milled. Apart from the step of bagging, no measures appear to be described to avoid spreading of asbestos into the environment, in particular not in the milling step.
DE-A-44 07 339 describes processing asbestos containing waste from buildings and building materials. The waste material is sealed inside a container, in particular a steel container. No other measures are taken to avoid spreading of asbestos particles into the environment.
GB-A-0 817 414 relates to the field of casting of titanium and other reactive metals. Vacuum is used for the removal of air (oxygen) from the room that surrounds the furnace.
AT-A-411818 describes the disposal of asbestos waste packed in pressure vessels by melting the pressure vessels in a furnace. The inside of vessels is sealed from the outside and as such no asbestos can escape before the waste is loaded into the furnace.
U.S. Pat. No. 5,662,050 describes a rotary kiln to treat toxic or hazardous waste and to produce “glass-like” or “ceramic-like” end products and useful metal products.
GB-A-2445420 relates to the treatment of hazardous waste components such as asbestos.
JP-A-2008/249220 describes melting and detoxifying asbestos-containing waste metal but does not describe the cooling of the molten metal or the recovery of said metal.
U.S. Pat. No. 5,370,066 describes an apparatus in which hazardous waste material is molten. The molten waste is solidified into inorganic ceramic-like aggregate material.
JP-A-2007/307548 is directed to a method for melting asbestos waste.
There still is a need for efficient and cost-effective methods that allow for processing of large quantities of asbestos-containing steel scrap without having to rely on the presence of other non-contaminated steel feeds and that is inherently safe in that the asbestos particles cannot spread into the environment. Such a method should not emit toxic compounds into the environment that are normally associated with asbestos and the processing thereof, such as polychlorinated biphenyls (PCBs), petroleum based products, paints, coatings, and the like.